The Universal Mobile Telecommunication Service (UMTS) standard provides a compatibility standard for cellular mobile telecommunications systems. The UMTS standard ensures that user equipment (UEs) operating in a UMTS system can obtain communication services when operating in a system manufactured according to the standard. To ensure compatibility, radio system parameters and data transfer procedures are specified by the standard, including protocols governing digital control messages and bearer traffic that are exchanged over an air interface.
The UMTS standards provide, in 3GPP TS 25.344 (Third Generation Partnership Project Technical Specification 25.344) v0.5.0, 3GPP TS 23.246 v1.1.0, 3GPP TS 23.846 v6.1.0, 3GPP TS 25.331 v5.6.0, and 3GPP TS 25.346 v0.5.0, for a provision of a Multimedia Broadcast/Multicast Service (an MBMS service) by a UMTS communication system to UEs serviced by the system and subscribed to the service. The MBMS service provides for a multicast and unicast of MBMS data, typically in a format of Internet Protocol (IP) data packets, to the subscribed UEs. In order to ensure that the air interface resources of the UMTS communication system are not wasted, the system first estimates the number of recipients, that is subscribed UEs, in a cell providing MBMS data. Based on the estimated number of recipients, a Radio Network Controller (RNC) included in a UMTS infrastructure determines whether to establish a Point-To-Multipoint (PTM) communication channel in the cell or a Point-To-Point (PTP) communication channel to each recipient.
When the RNC determines to establish a PTM communication channel, typically the RNC then multicasts the MBMS data via a Forward Access Channel (FACH) that is mapped to a Secondary Common Control Physical Channel (S-CCPCH). Currently, common physical channels such as the S-CCPCH are not power controlled. Furthermore, the RNC and the Node B are not aware of a specific geographic location of each subscribing UE serviced by the Node B. As a result, when the RNC establishes an S-CCPCH for a multicast of MBMS data, the RNC instructs the Node B to allocate a fixed percentage of the Node B's transmit power to the S-CCPCH, which percentage is sufficient to provide an acceptable error rate at the edge of the cell serviced by the Node B.
For example, for a 64 kilobits per second (kbps) service, achieving a target Block Error Rate (BLER) of one percent (1%) at the edge of a cell may require approximately 25% of a Node B's power. As a result, an MBMS service may consume an inordinate percentage of a Node B's total transmit power and may limit the Node B's ability to provide other communication services to other UEs serviced by the Node. B. Furthermore, allocation of such a high power level to the S-CCPCH increases the likelihood that the S-CCPCH will unacceptably interfere with communication channels allocated to other UEs engaged in active communications in neighboring cells. In addition, once power is allocated to the S-CCPCH, the allocated power remains static throughout the provision of the MBMS service regardless of any change in a location of one or more subscribing UEs and/or change in channel conditions. As a result, an allocation of a fixed amount of power to the S-CCPCH that is based on providing service to UEs located at an edge of a cell may be wasteful of a limited resource and may create undesirable levels of interference.
Therefore, a need exists for a method and apparatus that provides for an allocation to the S-CCPCH of a power level that is appropriate for the requirements of the UEs subscribing to an MBMS service and that further provides for a dynamic setting and adjustment of the allocated power.